An obvious intent of any automatic recovery system for almost any aircraft is to prevent ground impact during controlled flight of the aircraft. Many aircraft have standard proximity alarms for alerting pilots to the nearness of ground or water impact surfaces. These alarms can be based on inadmissible rates of descent of the aircraft or nearness of the ground. While proximity alarms are an improvement over prior instruments they are not a solution to many of problems that have been shown to cause aircraft ground impacts.
The need for ground collision avoidance extends to a wide variety of aircraft and scenarios ranging from terminal area navigation for commercial airliners to low level navigation, pilot spatial disorientation and g-induced loss of consciousness (GLOC) for high performance aircraft. While some aircraft have been equipped with ground proximity warning systems, these systems tend to be as much of a nuisance as an aid during flight. Most of the existing ground proximity warning systems contain no provisions for variations in aerodynamics, relying on the pilot to compensate for these variations by giving him a finite amount of time to recover level flight. At the same time these systems are passive, relying on pilot awareness and competence to recover from the situation.
Thus two essential problems remain with proximity warning systems. Firstly, if the pilot or crew is incapacitated, as might occur due to loss of cabin pressure after a bird strike through the cockpit windshield, for example, pilot awareness or ability may not be up to the task of controlling the aircraft and recovering level flight. Further, such conventional ground proximity warning systems contain insufficient provisions to account for variations in aircraft aerodynamics and flight state and reliably predict when aircraft flyups are required without setting off numerous nuisance alarms. Numerous nuisance alarms will often result in crews disabling such safety systems.
An innovative approach to this problem which appears to be a forward step in the art of aircraft auto recovery is disclosed in U.S. Pat. No. 4,058,710 to Altman. The Altman patent discloses a process for preventing unwanted contact by an aircraft with land or water. When applied over land the process assumes flat terrain or low hills. Altman's process utilizes the aircraft's rate of descent and altitude to compute a limiting altitude which is further modified by the aircraft's ability for transverse acceleration. This limiting altitude is used to determine when to activate an automatic feedback controller which provides the aircraft with the maximum feasible transverse acceleration. Thus the Altman device attempts to continuously calculate a limiting altitude for the aircraft below which automatic controls will be applied for aircraft recovery. Various theoretical schemes are proposed by Altman in this patent for determining this limiting altitude. All of these schemes however, appear to be either difficult to incorporate into an aircraft control design or simplified in a manner that will cause spurious effects including nuisance flyups during controlled flight.
A need therefore exists for a ground collis on avoidance system capable of calculating a decision height at which a recovery maneuver must be initiated in order to prevent aircraft penetration of a preset floor or ground impact.
A further need exists for a ground collision auto recovery system that is sufficiently sophisticated to initiate a recovery maneuver when required while avoiding a multitude of nuisance flyups that interfere with controlled flight.
Yet another need exists for a ground collision avoidance system which can be made at minimum cost and which can be developed for a multitude of aircraft.